This invention relates to cationically curable, optionally substituted, oxyalkylene ethers containing vinyl groups. The invention is directed, also, to methods for the synthesis of these oxyalkylene ethers and the use of these compounds as photochemically curable oligomers in casting compounds and coating agents and as reactive diluents for epoxide resins.
Aside from free radical polymerizing systems, in which curing is brought about by the action of UV, cationically curable systems containing epoxy or vinyl compounds have been developed in recent years. For these latter systems, curing is initiated particularly by diaryliodonium and triarylsulfonium salts. The advantages of cationically curing systems are that the curing reaction is insensitive to oxygen of the air, the film is cured rapidly and these systems do not contaminate the environment.
There is extensive patent literature dealing with this subject. The cationic curing of epoxy compounds with onium salts of 5th, 6th and 7th main groups of the periodic table is described, for instance, in the German Patents 25 18 656, 25 18 652 and 25 18 639. The cationic curing of vinyl monomers is the object of U.S. Pat. Nos. 4,617,238, 4,518,788 and 4,705,887.
Because they cure rapidly, can be processed economically and do not contaminate the environment, the UV-curable vinyl ether compounds have gained special attention. Such vinyl ether compounds can be synthesized in various ways. In a survey paper dealing with the "Rate-Determining Factors in Cationic UV Curing" in the journal Farbe und Lack, 1987, pages 803 to 807, the following possible reactions are given:
1. Base-catalyzed acetylene addition to diols according to Reppe ##STR2## 2. Phase transfer-catalyzed condensation of 2-chloroethyl vinyl ether with diols ##STR3## 3. Catalyzed rearrangement of bis-allyl ethers into the corresponding bis-propenyl ethers ##STR4##
The Reppe addition is not realizable from an economic point of view. For the second reaction, 2-chloroethyl ether is required, the use of which is undesirable for physiological reasons. It is common to all three types of reaction that invariably only one vinyl ether group per OH group of the alcohol can be introduced in to the molecule.